Among acid-fast bacilli, Mycobacterium tuberculosis is widely known, and one-third of the human population are said to be infected therewith. In addition to Mycobacterium tuberculosis, Mycobacterium africanum and Mycobacterium bovis are also known to be grouped in the Mycobacterium tuberculosis complex, and are known as mycobacteria, which are highly pathogenic to humans.
The treatment of these tuberculosis uses three agents, i.e., rifampicin, isoniazid, and ethambutol (or streptomycin), or four agents, i.e., the above three agents and pyrazinamide, which serve as first-line drugs.
However, the treatment of tuberculosis requires a distinctly long-term drug administration, which causes poor compliance, often resulting in treatment failure.
Further, the aforementioned agents have been reported to cause side effects as exemplified below: rifampicin causes hepatopathy, flu syndrome, and drug allergy, and is contraindicated for use in combination with other agents due to P450 related enzyme induction; isoniazid causes peripheral neuropathy and induces serious hepatopathy when used in combination with rifampicin; ethambutol causes failing vision due to optic neuropathy; streptomycin causes hearing deterioration due to eighth cranial nerve neuropathy; and pyrazinamide causes hepatopathy, gout attacks accompanied by an increase in the uric acid level, as well as vomiting, and the like (Non-patent Literature 1 and 2).
As a practical matter, cases have been reported where standard chemotherapy could not be performed due to the aforementioned side effects, which account for 70% of the cases where drug administration was discontinued (approximately 23%, 52 cases) of the total number of cases (228 hospital patients surveyed in all) (Non-patent Literature 3).
In particular, out of the above-mentioned five agents, which are used in combination as first-line drugs, rifampicin, isoniazid, and pyrazinamide commonly cause hepatotoxicity, which is known as the most frequently occurring side effect. Meanwhile, tubercle bacilli that are resistant to antituberculosis agents, tubercle bacilli that are resistant to multiple drugs, etc., have been increasing, making treatment more difficult.
A WHO survey (2008) reported that there are 390,000 to 510,000 patients with multidrug-resistant tuberculosis in the world, which account for 3.6% of the total number of tuberculosis patients, and that 5.4% of multidrug-resistant tuberculosis are equal to extensively drug-resistant tuberculosis (Non-patent Literature 4).
Further, one-third of HIV positive patients are suspected of being co-infected with tuberculosis; the number of such patients is said to be 14 million (Non-patent Literature 5). It is also reported that co-infection of HIV and tuberculosis poses a 20 to 37 times greater risk of developing tuberculosis than usual (Non-patent Literature 6).
In view of the above-described current status, examples of the profiles of a desired antituberculosis agent include (1) an agent that is also effective against multidrug-resistant tubercle bacilli; (2) an agent that enables short-term chemotherapy; (3) an agent with few side effects; (4) an agent that shows efficacy against latent infection with tubercle bacilli (latent tuberculosis); (5) an agent that can be administered orally; and the like.
Examples of bacteria known to be pathogenic to humans include pathogens of recently increasing MAC infections (Mycobacterium avium-intracellulare complex infections), such as Mycobacterium avium and Mycobacterium intracellulare; and other atypical acid-fast bacilli, such as Mycobacterium kansasii, Mycobacterium marinum, Mycobacterium simiae, Mycobacterium scrofulaceum, Mycobacterium szulgai, Mycobacterium xenopi, Mycobacterium malmoense, Mycobacterium haemophilum, Mycobacterium ulcerans, Mycobacterium shimoidei, Mycobacterium fortuitum, Mycobacterium chelonae, Mycobacterium smegmatis, and Mycobacterium aurum. 
At present, there are few promising therapeutic agents against atypical mycobacteriosis, and the current status is that an antituberculosis agent, such as rifampicin, isoniazid, ethambutol, streptomycin, and kanamycin, is used in combination with a therapeutic agent against general bacterial infections, such as a new quinolone agent, a macrolide antimicrobial agent, an aminoglycoside antimicrobial agent, and a tetracycline antimicrobial agent.
However, compared with the treatment of infections with common bacteria, the treatment of atypical mycobacteriosis requires long-term drug administration, and in some cases, according to reports, atypical mycobacteriosis become intractable, possibly causing death. In order to overcome the current status, the development of a drug with a higher efficacy is in demand.
For example, Patent Literature 1 discloses that a 6-nitro-1,2,3,4-tetrahydro[2,1-b]imidazopyran compound is useful as an antituberculosis agent, because the compound has bactericidal action in vitro against tubercle bacilli (H37Rv strain) and multidrug-resistant tubercle bacilli, as well as because the compound shows, when orally administered, a therapeutic effect on an animal model infected with tuberculosis.
Patent Literature 2 and 3 disclose that a 2,3-dihydroimidazo[2,1-b]oxazole compound has bactericidal action against tubercle bacilli, multidrug-resistant tubercle bacilli, and atypical acid-fast bacilli.
Patent Literature 4 discloses that nitroimidazooxazine and nitroimidazooxazole compounds can be used as a drug against Mycobacterium tuberculosis. 
However, the compounds disclosed in the above-mentioned literature have a structure different from that of the compounds of the present invention, and thus are dissimilar compounds.